Study On Absorption Selectivity Of Iron-based Composite Ionic Liquids For Acidic Gases

Traditional solvents have many shortcomings such as high energy consumption and high cost in the process of removing hydrogen sulfide and carbon dioxide.A new green wet desulfurization process is urgently needed to replace traditional organic solvents.In recent years,iron-based ionic liquids have become a research hotspot in the removal of acidic components in natural gas.In order to promote the new green desulfurization process,the iron-based ionic liquids were used as matrix,polyethylene glycol dimethyl ether(NHD)was selected as additives to prepare iron-based composite ionic liquids.By combining the absorption kinetics research method,the composite system was tested under different conditions.The desulfurization effect and absorption selectivity were discussed,and the absorption mechanism and kinetic characteristics of the desulfurization process with complex ionic liquid desulfurizer were discussed based on the theory of micro-kinetics.The main conclusions are as follows:(1)In this paper,NHD was added to BmimFeC14 in a ratio of 1:4 to obtain iron-based composite ionic liquids.The results of infrared spectroscopy,electrochemistry,viscosity,and thermogravimetric analysis before and after desulfurization show that the composite ionic liquid has good hydrophobicity and thermal stability.Proper temperature rise is conducive to the continuous desulfurization of desulfurizer,reducing the viscosity of the system and increasing the reaction rate of hydrogen sulfide absorption.(2)The absorption of carbon dioxide by composite ionic liquids is a physical absorption process.Its absorption decreases with the increase of temperature and increases with the increase of pressure.The maximum absorption load of carbon dioxide is 0.299 mol/L(0.6 MPa,298.15 K);the absorption of hydrogen sulfide by composite ionic liquids is mainly a chemical absorption process,and the maximum absorption load of hydrogen sulfide is 1.418 mol/L(0.9 MPa,303.15 K).The maximum absorption rates of hydrogen sulfide and carbon dioxide were 0.04(mol/L.5 min)(298.15 K,0.06 MPa)and 0.017(mol/L.5 min)(298.15 K,0.06 MPa),respectively.The absorption rates of hydrogen sulfide were 2.3 times of that of carbon dioxide at the same temperature and pressure.(3)The maximum adsorption capacity of hydrogen sulfide and carbon dioxide in competitive absorption is 0.433 mol/L(0.5 MPa,313.15 K)and 0.217 mol/L(0.4 MPa,293.15 K),respectively;the absorption load of hydrogen sulfide will seriously affect the absorption of carbon dioxide in the composite system,while the absorption load of carbon dioxide has a weak influence on the absorption of hydrogen sulfide in the composite system;when the two mixtures absorb at the same concentration,the absorption of hydrogen sulfide is due to the absorption of hydrogen sulfide.It dissolves in ionic liquids before carbon dioxide,which saturates the hydrogen bond and hinders the absorption of carbon dioxide.(4)Hydrogen sulfide is rapidly dissociated and oxidized when complex ionic liquids absorb hydrogen sulfide at the initial stage.With the reaction proceeding,a large number of sulfur ions and sulfur are formed.At the later stage of the reaction,the acidity of the complex system increases,and hydrogen sulfide can hardly dissociate,which results in absorption stopping.The addition of NHD effectively reduces the viscosity of the complex system and makes hydrogen sulfide gas easier to pass through the phase boundary.The surface enters the liquid phase and promotes the chemical reaction process of desulfurization.(5)The kinetics of hydrogen sulfide absorption by composite ionic liquids was studied.According to the characteristics of hydrogen sulfide in natural gas,the reaction absorption kinetics equation of hydrogen sulfide was established.Under experimental conditions,the process of hydrogen sulfide absorption by composite ionic liquids was a fast pseudo-first-order reaction,and the desulfurization process was mainly controlled by liquid membrane,improving mass transfer coefficient,lowering temperature,accelerating stirring and compounding high transmission.The desulfurization process can be effectively optimized by mass-rate solvents.